This invention relates to aerosol metering valves, by which term is meant a valve intended to be secured in a fluid-tight manner to a container for a pressurized liquid intended to be dispensed in fixed amounts per dispensation.
The liquid to be dispensed (product) may be a liquefied gas generating sufficient vapor pressure to dispense itself when the valve is opened. Liquids which are not this volatile may have a fluid propellant added to them. When the vapor pressure drops, sufficient of the propellant boils off to provide additional vapor, so that the discharge pressure is kept virtually constant irrespective of the amount of product in the container. The product may be only a liquid, but when the container is intended to dispense controlled amounts of a medicament, the latter may take the form of a powered solid which is suspended in the liquid carrier, or dissolved in it. Such solutions or suspensions are included in the term `liquid product` or just simply `product`.
In order to avoid the need for a dip tube to convey product up to the valve so that the product may be dispensed when the container is upright, with the valve on top, known containers are intended to be turned upside-down before the valve is opened. This ensures that only liquid product passes through the valve until the product is almost exhausted, at which stage some gas is discharged with the liquid.
When the container is turned upright after a dispensation, the liquid product in a constant-volume (metering) chamber forming part of the valve tends to drain back into the container, being replaced by the propellant gas or vapor. Thus when the container is next inverted for a fixed volume of product to be dispensed, opening the valve has to be deferred for a period sufficient to permit all the gas in the metering chamber to be replaced by liquid. In addition, if the product to be dispensed is a suspension, while the carrier liquid may drain back, the suspended particles would tend to be trapped in the passages leading from the metering chamber. This is highly undesirable, because when a fresh charge of product enters the metering chamber, it has the residual particles suspended in it, so that its concentration varies, and the user loses control of the amount of medicament dispensed during each operation. If the time allowed for recharging is insufficient, the chamber contains a mixture of liquid and gas at the time the valve is opened, so that less than the predetermined volume of liquid is dispensed.
In order to fill the container after the metering valve has been secured to the open mouth of the container by crimping, fresh product is introduced via a passage under such pressure that a sealing gasket is flexed sufficiently to break the fluid seal between it the and an operating rod. When this filling pressure is removed, the gasket resiles into its sealing position. This being already known, it will not be further described herein.
The present invention aims at providing an aerosol metering valve containing a fixed-volume metering chamber out of which liquid product cannot drain under gravity when a container to which the valve is sealed is upright.